Investigation on Fracture Behavior of Modified 9Cr-1Mo Steel Base and Welded Joint in As-Weld and Post-Weld Heat-Treated Condition

Fracture resistance behavior of Mod. 9Cr-1Mo steel base and its all-weld metal in as-weld and post-weld heat-treated (PWHT) conditions has been investigated at room temperature, 350, 450 and 550 °C. The fracture resistance behavior and fracture toughness (JIc) of the weld joint have been evaluated as per ASTM E 1820 and ISO 15653. The base metal’s fracture toughness decreased with rising temperature from 352 kJm−2 at room temperature to 248 kJm−2 at 550 °C. The as-welded metal exhibited brittle fracture across all test temperatures. Its fracture toughness was significantly low, ranging from 13 to 17 kJm−2. PHWT improved the weld metal’s fracture toughness; values ranged from 468 to 256 kJm−2, with the lowest toughness of 256 kJm−2 at 350 °C. The fractography studies reveal ductile dimples in both the base metal and PWHT specimens, and cleavage facets in as-welded specimens with few small dimples. Additionally, a sharp gradient in hardness profile across the weld interface further confirms the brittle nature of the as-weld joint.